In a semiconductor apparatus with a built-in power supply circuit for LEDs used as a backlight of an LCD panel of a cellular phone, for example, the size of IC packaging should be minimized in order to reduce the size of the apparatus. Thus, it is important to reduce the number of terminals used in an IC package. In one method, the number of such terminals may be reduced by assigning multiple functions to a single IC terminal.
For example, in a conventional semiconductor apparatus, a clock signal is supplied to a triangular wave oscillating circuit via a clock signal input terminal, which is an external terminal of the semiconductor apparatus, to generate a triangular wave voltage used for the PWM (pulse wave modulation) control of a switching regulator (see Japanese Laid-Open Patent Application No. 2006-101663, for example). The clock signal is also supplied to a clock pulse detection circuit. The clock pulse detection circuit generates a standby signal if the clock signal remains at a low level for a certain duration of time, thereby terminating the operation of the switching regulator. Thus, the clock signal input terminal doubles as a standby signal input terminal of the switching regulator. However, such a system cannot be utilized when the clock signal of the triangular wave oscillating circuit is generated within the semiconductor apparatus.
Thus, there is a need for a semiconductor apparatus including a power supply circuit, such as a switching regulator, having a reduced number of terminals, wherein a clock signal of a triangular wave oscillating circuit is generated within the semiconductor apparatus. There is also a need for a method of controlling an operation of such a semiconductor apparatus.
In one aspect of the present invention, a semiconductor apparatus includes an input terminal to which an input voltage is applied; an output terminal at which an output voltage is obtained; a power supply circuit unit configured to generate the output voltage from the input voltage, the output voltage having a value corresponding to a duty cycle of a voltage setting signal that is externally applied to the semiconductor apparatus; and a determination circuit unit configured to determine whether the voltage setting signal has a predetermined signal level for the duration of a first predetermined time or longer. The determination circuit unit, when it determines that the voltage setting signal does not have the predetermined signal level for the duration of the first predetermined time or longer, activates the power supply circuit unit, and deactivates the power supply circuit unit when it determines that the voltage setting signal has the predetermined signal level for the duration of the first predetermined time or longer.
In another aspect of the present invention, a method of controlling an operation of a semiconductor apparatus includes generating an output voltage at an output terminal of the semiconductor apparatus from an input voltage applied to an input terminal of the semiconductor apparatus, the output voltage having a value corresponding to a duty cycle of a voltage setting signal externally applied to the semiconductor apparatus; determining whether the voltage setting signal has a predetermined signal level for the duration of a first predetermined time or longer; supplying the output voltage to the output terminal of the semiconductor apparatus when the determining step determines that the voltage setting signal does not have the predetermined signal level for the duration of the first predetermined time or longer; and not supplying the output voltage to the output terminal when the determining step determines that the voltage setting signal has the predetermined signal level for the duration of the first predetermined time or longer.